Question

我有两张桌子：

用户
帖子

帖子属于用户，帖子可以授予其他用户。如何在rails模型中映射此关联？

这些是我目前无关的协会：

class Post < ActiveRecord::Base

    belongs_to :user
    has_one :awarded_user, :class_name => 'User', :foreign_key => 'awarded_to_user_id'

当我尝试访问post.awarded_user时，我在rails控制台中收到此错误：

ActiveRecord::StatementInvalid: Mysql2::Error: Unknown column 'users.awarded_to_user_id' in 'where clause': SELECT  `users`.* FROM `users` WHERE `users`.`awarded_to_user_id` = 8 LIMIT 1

查询会搜索user.awarded_to_user_id但是，我需要它在posts中搜索成为posts.awarded_to_user_id。

我该如何解决这个问题？

Answer 1

首先，生成一个将列添加到posts表中的迁移。

class AddAwardedToUserIdToPosts < ActiveRecord::Migration                   
  def change                                                                
    add_column :posts, :awarded_to_user_id, :integer, index: true
  end                                                                      
end

现在，在您的模型中：

class User < ActiveRecord::Base                                             
  has_many :posts                                
  has_one :awarded_post, class_name: 'Post', foreign_key: 'awarded_to_user_id'  
end

适用于Post

class Post < ActiveRecord::Base                                             
  belongs_to :awarded_user, class_name: 'User', foreign_key: 'awarded_to_user_id'
  belongs_to :user
end

现在，在这种情况下，你可以实现你所说的：

user_zaid = User.create first_name: "Zaid"
user_ali = User.create first_name: "Ali"

post = Post.create description: "A less descriptive post"

post.user = user_zaid
post.awarded_user = user_ali

post.save


# Or the other way

user_ali.posts << post # Since, user has_many posts.
user_ali.awarded_post = post # Since, user has_one awarded_post. 

user_ali.save

# How to fetch:

User.last.posts # it will give you the posts.
User.last.awarded_post # it will give you the (single) awarded post.

对于Post，

Post.last.user # it will give you the user which it belongs to
Post.last.awarded_user # it will give you the user which it was **awarded** to

将一个表中的单个列引用到另一个表

1 个答案: